Retaining ring having inner surfaces with features

ABSTRACT

Some implementations of a retaining ring has an inner surface having a first portion formed of multiple planar facets and a second portion that adjoins the first portion along a boundary and includes a frustoconical surface that is sloped downwardly from outside in. Some implementations of the retaining ring have a crenellated or serpentine inner surface, and/or an inner surface with alternating region of different surface properties or different tilt angles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application and claims priority to U.S.application Ser. No. 14/992,763, filed on Jan. 11, 2016, which claimspriority to U.S. Application Ser. No. 62/168,578, filed on May 29, 2015,which are incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to chemical mechanicalpolishing of substrates, and more particularly to retaining rings foruse in chemical mechanical polishing.

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive or insulative layerson a silicon substrate. One fabrication step involves depositing afiller layer over a non-planar surface, and planarizing the filler layeruntil the non-planar surface is exposed. For example, a conductivefiller layer can be deposited on a patterned insulative layer to fillthe trenches or holes in the insulative layer. The filler layer is thenpolished until the raised pattern of the insulative layer is exposed.After planarization, the portions of the conductive layer remainingbetween the raised pattern of the insulative layer form vias, plugs andlines that provide conductive paths between thin film circuits on thesubstrate. In addition, planarization may be needed to planarize adielectric layer at the substrate surface for photolithography.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head of a CMP apparatus.The exposed surface of the substrate is placed against a rotatingpolishing disk pad or belt pad. The polishing pad can be either a“standard” pad or a fixed-abrasive pad. A standard pad has a durableroughened surface, whereas a fixed-abrasive pad has abrasive particlesheld in a containment media. The carrier head provides a controllableload on the substrate to push it against the polishing pad. A polishingslurry, including at least one chemically-reactive agent, and abrasiveparticles if a standard pad is used, is supplied to the surface of thepolishing pad.

The substrate is typically retained below the carrier head by aretaining ring. However, because the retaining ring contacts thepolishing pad, the retaining ring tends to wear away, and isoccasionally replaced. Some retaining rings have an upper portion formedof metal and a lower portion formed of a wearable plastic, whereas someother retaining rings are a single plastic part.

SUMMARY

In one aspect, a retaining ring includes an annular body that has a topsurface configured to be secured to a carrier head, a bottom surfaceconfigured to contact a polishing surface, an outer surface extendingfrom the top surface at an outer top perimeter to the bottom surface atan outer bottom perimeter, and an inner surface extending from the topsurface at an inner top perimeter to the bottom surface at an innerbottom perimeter. The inner surface includes a first portion adjacentthe bottom surface and a second portion adjoining the first portionalong a boundary. The first portion comprises seven or more facets. Theinner bottom perimeter is defined by bottom edges of the facets. Thesecond portion may include a frustoconical surface that is slopeddownwardly from outside in.

Implementations may include one or more of the following features. Thefacets may be planar. Adjacent facets may be being connected at astraight side edge. The inner bottom perimeter may be defined bystraight bottom edges of the planar facets. The boundary may include aplurality of curved edges corresponding to the plurality of facets, andeach curved edge for a facet may have a lowest point at a horizontalcenter of the facet. The annular body may include an upper portion and alower portion of a different material than the upper portion. A lowestpoint on each curved edge may be aligned to a boundary between the upperportion and the lower portion. The bottom surface may include channelsextending from the outer surface to the inner surface. Each channel mayhave an end open to the inner surface of the body at a straight sideedge. The inner surface may include a first number of facets and thebottom surface may have a second number of channels, and the firstnumber may be a whole number multiple of the second number. The wholenumber may be three, four or five. The inner surface may have a total of72 facets. The inner bottom perimeter may be is a regular polygon.

In another aspect, a retaining ring includes an annular body that has atop surface configured to be secured to a carrier head, a bottom surfaceconfigured to contact a polishing surface, an outer surface extendingfrom the top surface at an outer top perimeter to the bottom surface atan outer bottom perimeter, and an inner surface extending from the topsurface at an inner top perimeter to the bottom surface at an innerbottom perimeter. The inner surface includes a plurality ofinwardly-extending projections, each projection having a flat innermostsurface.

In another aspect, a retaining ring includes an annular body that has atop surface configured to be secured to a carrier head, a bottom surfaceconfigured to contact a polishing surface, an outer surface extendingfrom the top surface at an outer top perimeter to the bottom surface atan outer bottom perimeter, and an inner surface extending from the topsurface at an inner top perimeter to the bottom surface at an innerbottom perimeter. The inner surface includes a plurality ofinwardly-extending projections, the projections providing the innerbottom perimeter with a serpentine path.

In another aspect, a method of forming a retaining ring includes joiningan upper portion of the retaining ring having a frustoconical innersurface to a lower portion of the retaining ring having a cylindricalinner surface, and machining the inner surface of the lower portion andthe inner surface of the upper portion to form a plurality of flatfacets that intersect the frustoconical surface at a plurality of curvededges.

Implementations may include one or more of the following features. Theinner surfaces may be machined such that a lowest point on each curvededge is aligned to a boundary between the upper portion and the lowerportion. The inner surfaces may be machined such that a lowest point oneach curved edge is above a boundary between the upper portion and thelower portion. Joining may include one or more of adhering with anadhesive, connecting with a mechanical fastener, or fixing with adovetail joint.

In another aspect, a retaining ring includes an annular body that has atop surface configured to be secured to a carrier head, a bottom surfaceconfigured to contact a polishing surface, an outer surface extendingfrom the top surface at an outer top perimeter to the bottom surface atan outer bottom perimeter, and an inner surface extending from the topsurface at an inner top perimeter to the bottom surface at an innerbottom perimeter. The inner surface includes a plurality of regionsspaced angularly around the annular body, the plurality of regionshaving different surface textures.

Implementations may include one or more of the following features. Theplurality of regions may be arranged in a regular pattern. The differentsurface textures may include different roughnesses. The differentroughnesses may include a first roughness having an Ra between 4 and 64microinches and a second roughness that is less than the firstroughness. The different surface textures may include surface groovingin different directions. The different directions may be perpendicular.One of the different directions may be parallel or perpendicular to theinner bottom perimeter. The different surface textures may includesurface grooving having different depths.

In another aspect, a retaining ring includes an annular body that has atop surface configured to be secured to a carrier head, a bottom surfaceconfigured to contact a polishing surface, an outer surface extendingfrom the top surface at an outer top perimeter to the bottom surface atan outer bottom perimeter, and an inner surface extending from the topsurface at an inner top perimeter to the bottom surface at an innerbottom perimeter. The inner surface includes a plurality of regionsspaced angularly around the annular body, the plurality of regionshaving different tilts relative to the bottom surface.

Implementations may include one or more of the following features. Theplurality of regions may be are arranged in a regular pattern. One ofthe different tilts may be perpendicular to the bottom surface. Thedifferent tilts may include a first tilt that is slanted inwardly frombottom to top and a second tilt that is slanted outwardly from bottom totop.

Advantage may include the following. An edge of a substrate beingpolished can contact the retaining ring at multiple points. Thuspressure on the substrate edge can be distributed over a wider region,or rotation of the substrate can be improved. Consequently, the polishedsubstrate can achieve better thickness uniformity, e.g., less angularasymmetry. The retaining ring can undergo lower wear, and consequentlyhave a longer lifetime.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other aspects, features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a carrier head.

FIG. 2 is a schematic top perspective view of a retaining ring.

FIG. 3 is a schematic bottom perspective view of the retaining ring ofFIG. 2.

FIG. 4 is a schematic planar top view of the retaining ring of FIG. 2.

FIG. 5 is a schematic planar bottom view of the retaining ring of FIG.2.

FIG. 6 is a schematic close-up perspective view of the retaining ring ofFIG. 2.

FIG. 7 is a schematic cross-sectional side view of the retaining ring ofFIG. 2.

FIGS. 8-12 are schematic cross-sectional planar views of a portion of aretaining ring having other geometries for the interior surface.

FIG. 13 is a schematic cross-sectional planar view of a portion of aretaining ring having an inner surface with regions of different surfacetexture.

FIG. 14 is a schematic perspective view of a portion of a retaining ringhaving an inner surface with regions of different surface texture.

FIG. 15 is a schematic perspective view of a portion of a retaining ringhaving an inner surface with regions of different inclination.

FIG. 16 is a schematic cross-sectional side view of retaining ringhaving an insert to provide the inner surface that contacts thesubstrate.

Similar reference number in the drawings represent similar features.

DETAILED DESCRIPTION

A retaining ring in a CMP apparatus has an inner surface that confinesmovement of a substrate being polished by the CMP apparatus. In aconventional retaining ring, the inner surface has a circular perimeter.In contrast, some implementations of the retaining ring described hereinhave an inner surface formed of multiple planar facets, with adjacentfacets joined at corners. Some implementations of the retaining ringdescribed herein have a crenellated or serpentine inner surface, and/oran inner surface with alternating region of different surface propertiesor different tilt angles. This can improve the thickness uniformity ofthe polished substrate.

Referring to FIG. 1, a retaining ring 100 is a generally an annular ringthat can be secured to a carrier head 50 of a CMP apparatus. A suitableCMP apparatus is described in U.S. Pat. No. 5,738,574 and suitablecarrier heads are described in U.S. Pat. Nos. 6,251,215, and 6,857,945.The retaining ring 100 fits into a loadcup for positioning, centering,and holding the substrate at a transfer station of the CMP apparatus.

As an example, FIG. 1 shows a simplified carrier head 50 onto which theretaining ring 100 is secured. The carrier head 50 includes a housing52, a flexible membrane 54, a pressurizable chamber 56, and theretaining ring 100. The flexible membrane provides a mounting surfacefor a substrate 10. When the substrate 10 is mounted, the mountingsurface can directly contact a back surface of the substrate. In theexample shown in FIG. 1, the membrane 54 is clamped between theretaining ring 100 and the housing 52, but in some implementations, oneor more other parts, e.g., clamp rings, can be used to hold the membrane54.

The pressurizable chamber 56 is located between the membrane 54 and thehousing 52 can be pressurized, e.g., using a fluid (gas or liquid), topush a front surface of the substrate 10 against a polishing surface 62of a polishing pad 60 to polish the front surface. In someimplementations, the pressure in the chamber 56, and thus the downwardpressure of the flexible membrane 54 on the substrate 10, can becontrolled using a pump (not shown) that is fluidly connected to thechamber 56 though a passage in the housing.

The retaining ring 100 is secured near the edge of the housing 52 toconfine the substrate 10 below the membrane 54. For example, theretaining ring 100 can be secured by mechanical fasteners 58, e.g.,screws or bolts, that extend through passages 59 in the housing 52 intoaligned threaded receiving recesses in a top surface of the retainingring 100. Additionally, the top surface can have one or more alignmentapertures positioned to mate to a corresponding pin on the carrier headto allow proper alignment when the retaining ring 100 is secured to thecarrier head.

A drive shaft 80 can be provided to rotate and/or translate the carrierhead 50 across a polishing pad 60. In some implementations, the driveshaft 80 can be raised and lowered to control the pressure of a bottomsurface of the retaining ring 100 on the polishing pad 60.Alternatively, the retaining ring 100 can be movable relative to thedrive shaft 80 and the carrier head 50 can include an internal chamberwhich can be pressurized to control a downward pressure on the retainingring 100, e.g., as described in U.S. Pat. Nos. 6,183,354 or 7,575,504.

Referring to FIGS. 2-5, a top surface 110 of the retaining ring 100 ismostly flat, but includes a plurality of threaded recesses 112 toreceive the fasteners to hold the retaining ring 100 to the carrierhead. Optionally, the top surface 110 can have one or more alignmentfeatures, e.g., recesses 114, positioned to mate to a correspondingfeatures, e.g., projections, on the carrier head to allow properalignment when the retaining ring 100 is secured to the carrier head.Optionally, the top surface can include a raised outer rim where therecesses for the fasteners are located. Optionally, the top surface caninclude a plurality of concentric ridges extending around the ring,e.g., to grip the membrane 54.

A bottom surface 120 of the retaining ring 100 is configured to contactthe polishing surface of the polishing pad. Optionally, the bottomsurface 120 can include channels 122 that extend partially through thethickness of the retaining ring 100. Other than the channels 122, thebottom surface 120 can be flat and can be parallel to the upper surface110. In the example shown in FIGS. 2-5, the bottom surface 120 includeseighteen channels 122, although there can be a different number ofchannels, e.g., four to one hundred channels. In operation, the channels122 permit a polishing fluid, such as slurry, which can includeabrasives or be abrasive-free, to flow underneath the retaining ring 100to the substrate.

The channels 122 can be generally straight, and extend from an innersurface 130 to an outer surface 140 of the retaining ring 100. Thechannels 122 can be distributed at equal angular intervals around theretaining ring 100. The channels 122 are typically oriented at an angleα, e.g., between about 30° to about 60°, or about 45°, relative to aradial segment (R) extending through the center of the retaining ring100 and the channel, but alternatively the channels 122 can extend alongthe radial segment (R), i.e., 0° angle.

Each channel 122 can have a width W (see, FIG. 5) of about 0.75 mm toabout 25 mm, e.g., about 3.125 mm. The ratio of the width of the channelto the width of the spacing between channels can be between 10/90 and50/50. The channels can have a uniform width along their radial length,or could vary in width along their radial length, e.g., be flared at theinner and/or outer diameter. The various channels 122 can all have thesave width profile, or different channels can have different widths.Rather than a linear segment, the channels can be curved.

The sidewalls 124 of the channels 122 can be perpendicular to the bottomsurface 120, or can be at an angle less than 90°, e.g., at angle of45-85°, relative to the bottom surface 120. In some configurations, theedges 126 where the sidewalls 124 intersect the bottom surface 120, havea radius of curvature or a chamfer that is greater than about 0.1 mm butless than the height of the channel 122. The channels 122 can have adepth that is between 25% and 90% of the thickness of a lower portion102 of the retaining ring (see FIG. 7).

The total thickness of the retaining ring 100, e.g., between the topsurface 110 and the bottom surface 120 can be about 12.5 mm to about37.5 mm.

Referring to FIGS. 2, 3 and 7, at least a portion 142 of the outersurface 140 of the retaining ring 100 adjacent the bottom surface 120can be a vertical cylindrical surface having a circular shape in a topor bottom planar view. In some implementations, the retaining ring 100includes an overhanging portion 145; a bottom of the overhanging portion145 defines a horizontal portion 146 of the outer surface 140. Thishorizontal portion 146 can provide a lip to assist with centering theretaining ring in a substrate loader or to provide a hard stop for theretaining ring against the top inner edge of a surrounding ring.

The outer surface 140 can include a sloped portion 144, e.g., afrustoconical surface angled downwardly from the outside in, thatconnects the vertical cylindrical portion 142 to the horizontal portion146. A portion 148 of the outer surface 140 of the retaining ring 100adjacent the top surface 110 can be a vertical cylindrical surface. Thecylindrical portion 142 of the outer surface 140 adjacent the topsurface 110 outer surface 140 can have a larger diameter than thecylindrical portion 142 adjacent the bottom surface 120.

Referring to FIGS. 2, 3, 6 and 7, instead of a cylindrical surface, theportion 132 of the inner surface 130 adjacent the bottom surface 120 isformed of multiple facets 150. Each facet is a flat vertical surface andjoins an adjacent facet along a vertical edge 152. The flat verticalsurface in each facet can be substantially perpendicular to the bottomsurface 120. In some configurations, the thickness of the portion 132 inthe vertical direction is greater than the depth of the channel 122, asshown in FIG. 6.

The facets 150 intersect the bottom surface 120 along straight loweredges 154. The straight edges 154 of the facets 150 along the bottomsurface 120 connect to one another at the corners. Thus, in a bottomplanar view, the connected lower edges 154 can form a polygon (thenumber of facets is large enough that this polygon structure is notvisible in FIG. 5). The angle between each pair of adjacent facets canbe the same, so that the connected lower edges 154 form a regularpolygon.

In the example illustrated, the portion 132 of the inner surface 130 hasseventy two facets 150. However, there the retaining ring 100 could haveten to one-hundred and fifty facets. For example, the retaining ring 100could have twenty-five to one-hundred facets, e.g., sixty to eightyfacets. In some implementations, the retaining ring 100 has seventy-twofacets. An advantage of having about seventy-two facets is that itappears to provide superior polishing uniformity.

In the example illustrated, each facet 150 has the same width (distancealong the lower edge 154). However, in some implementations, some facetshave different widths than other facets. For example, the facets can bearranged with the wider facets arranged in a regular pattern, e.g.,every other facet or every third facet. Similarly, in the exampleillustrated, each facet 150 has the same height, but in someimplementations, some facets have different heights than other facets.

The number of facets 150 can be a whole number multiple of the number ofchannels 122. For example, one channel 122, may be provided for everytwo, three, four or five facets 150 on the inner surface 130. In someimplementations, each channel 122 in the bottom surface 120 intersectsthe inner surface 130 at an edge 152 between adjacent facets 150.Alternatively, each channel 122 in the bottom surface 120 couldintersect the inner surface 130 in a region formed between the edges 152that define a particular facet 150, i.e., the channel does not overlapan edge 152 between adjacent facets 150.

On average, the width of the bottom surface 120 of the retaining ring100, i.e., the distance between the inner surface 130 and the outersurface 140, is about 2.5 cm to about 5.0 cm.

A portion 134 of the inner surface 130, located above the portion 132,has a circular cross-section in the plane parallel to the bottom surface120. This portion 134 can be adjacent the top surface 110 and extenddownwardly. This portion 134 can be sloped, e.g., be a frustoconicalsurface angled downwardly from the outside in.

Each flat facet 150 intersects the conical surface of the portion 134along a curved edge 156. In particular, the facets 150 are taller attheir adjoining edges 152 than at their lateral centers—i.e.,equidistant from the opposite edges 152. That is, the curved edge 156dips downwardly away from each edge 152, with a lowest point that isequidistant from the opposite edges 152 of the facet 150. Assuming thesurface 134 is frustoconical and the facets 150 are vertical, then eachcurved edge 156 will define a hyperbolic curve.

Returning to FIG. 1, the inner surface 130 of the retaining ring 100, inconjunction with the lower surface of the flexible membrane 54, definesa substrate receiving recess 90. The retaining ring 100 prevents thesubstrate 10 from escaping the substrate receiving recess 90.

Generally, the substrate is circular and has a diameter of about 200 mmto about 300 mm. The size of the recess 90 in a top or bottom planarview is generally larger than surface area of the substrate 10 such thatthe substrate 10 can move its position relative to the retaining ring100. For the purpose of discussion, an inner radius (IR) of theretaining ring 100 is defined in the planar view of the retaining ringto be a distance between the center C of the retaining ring 100 to acenter point of a facet 150 that is equidistant between two oppositeedges 152. The inner diameter (twice the inner radius IR) is slightlylarger the substrate radius, e.g., by about 1 to 5 mm. For example, fora 300 mm diameter substrate, the retaining ring can have an innerdiameter of about 301 to 305 mm.

During a polishing process, the carrier head 50, including the retainingring 100, moves relative to the polishing pad 60. Friction of thepolishing pad 60 against the substrate 10 forces the substrate 10against the inner surface 130 of the retaining ring 100. Due to thefaceted structure, for at least some periods of time, the substrate 10contacts at least two facets 150 of the inner surface 130.

However, because the radius of the substrate 10 is smaller than theradius of the inner surface 130 of the retaining ring 100, the substrate10 and the inner surface 130 have different angular velocities. As aresult, the pair (or tuple, etc.) of facets 150 that contact thesubstrate 10 will shift over time. In other words, the retaining ring100 rotates relative to the substrate 10.

The wear of the inner surface 130 of the retaining ring 100 can bereduced or be distributed more evenly around the retaining ring ascompared to a retaining ring having a cylindrical inner surface thatcontacts the substrate 10. Without being limited to any particulartheory, when the inner surface of a retaining ring is cylindrical, asubstrate having a circular outer perimeter contacts the inner surfaceat a single location. In contrast, the multiple contacts can permit theforce of the substrate 10 against the inner surface 130 to bedistributed more widely, thus reducing the total force at any specificpoint and reducing the wear. The reduced wear can allow the retainingring to have an increased life expectancy.

Again without being limited to any particular theory, during therelative movement between the retaining ring 100 and the substrate 10,the substrate makes no direct point-to-point contact with any of thechannels 132 or channel openings located at the edges 152 between thefacets 150. Generally, the channels 130 can form high stress areas inthe retaining ring 100, where the retaining ring tends to be damaged orbreak more easily than other parts of the ring. By eliminating directpoint-to-point contacts between the channels 130 and the substrate 10,the high stress areas can be protected from direct impact of thesubstrate 10, and the likelihood of damage to the retaining ring can bereduced. As a result, the wear of the retaining ring is reduced and theretaining ring can be used for a longer period of time.

In some polishing processes, the relative movement between the substrate10 and the retaining ring 100 can reduce asymmetry in a polishedsubstrate and improve within-wafer uniformity. In a polished substratewith asymmetry, the polished substrate has a thickness variation thatvaries with the angular coordinate. Again without being limited to anyparticular theory, as compared to a single contact situation, themultiple contacts between the substrate 10 and the retaining ring 100can allow the substrate 10 to rotate relative to the carrier head 50,thus angularly spreading the effect of any asymmetric pressuredistribution from the carrier head 50, and thereby reducing thelikelihood or amount of asymmetry.

At least a lower portion 102 of the retaining ring 100 with the bottomsurface 120 can be formed from a material that is chemically inert tothe CMP process. The material should be sufficiently elastic thatcontact of the substrate edge against the retaining ring 100 does notcause the substrate to chip or crack. However, the material should notbe so elastic as to extrude into the substrate receiving recess when thecarrier head puts a downward pressure on the retaining ring 100. Thematerial of the lower portion 102 should also be durable and have a lowwear rate, although it is acceptable for the lower portion 102 of theretaining ring 100 to wear away.

For example, the lower portion 102 of the retaining ring 100 can be madeof a plastic that is chemically inert in a CMP process. The plastic canhave a durometer measurement of about 80-95 on the Shore D scale. Ingeneral, the elastic modulus of the plastic can be in the range of about0.3-1.0×10⁶ psi. Suitable plastic can include (e.g., consist of)polyphenylene sulfide (PPS), polyaryletherketone (PAEK),polyetheretherketone (PEEK), polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polytetrafluoroethylene (PTFE),polybenzimidazole (PB polyetherimide (PEI), polyetherketoneketone(PEKK), polybutylene naphthalete (PBN), polyvinyl chloride (PVC),polycarbonate, a combination of one or more of these plastics, or acomposite material, e.g., one or more of these plastics and a filler,for example, glass or carbon fibers. An advantage of polyphenol sulfide(PPS) is that it is reliable and commonly used material for retainingrings.

An upper portion 104 of the retaining ring 100 can be made of a materialthat is at least as rigid as the lower portion 102. In someimplementations, the upper portion 104 can be made of a material that ismore rigid than the lower portion 102. For example, the upper portion104 can be a metal, e.g., aluminum or stainless steel, or a ceramicmaterial, or a plastic that is more rigid than the plastic of the lowerportion 102. In some implementations, the upper portion 104 has aboutthe same rigidity as the lower portion, e.g., within 2%, but is of lowerquality, e.g., a greater rate of contaminants, internal defects such asinclusions or voids, and is thus less expensive.

An adhesive, e.g., an epoxy can be used to join the lower portion 102 tothe upper portion 104. Alternatively or in addition, mechanicalfasteners and/or a dovetail joint could be used to join the lowerportion 102 to the upper portion 104.

In some implementations, the lowest point on the curved edge 156 betweena facet 150 and the conical portion 134 of the inner surface can bealigned, i.e., at the same height, as the boundary between the upperring 104 and the lower ring 102. However, in some implementations thelowest point on the curved edge 156 is above the boundary between theupper ring 104 and the lower ring 102.

To fabricate the retaining ring, the upper ring 104 can be formed withthe frustoconical inner surface 134, and the lower ring 102 can beformed with a vertical cylindrical surface. The lower ring 102 is joinedto the upper 104. Then the inner surface 130 is machined to form thefacets 150. The upper ring 104 and the lower ring 102 can be formed bymachining an appropriate block of material, or by injection molding.

The retaining ring 100 can also have other features or featuresalternative to those discussed above. In some implementations, theretaining ring 100 has one or more through holes that extendhorizontally or at a small angle from horizontal through the body of theretaining ring from the inner surface to the outer surface for allowingfluid, e.g., gas or liquid, to pass from the interior to the exterior,or from the exterior to the interior, of the retaining ring duringpolishing. The through-holes can be evenly spaced around the retainingring.

In some implementations, one or more surfaces of the retaining ring,e.g., the inner surface 130 and/or the outer diameter surface 140 can becoated with a film. The film can be a hydrophobic or hydrophilic film,and/or can serve as a protective film. For example, the film can bepolytetrafluoroethylene (PTFE) or diamond-like carbon.

In addition to the flat faceted regular polygon described with respectto FIGS. 1-7, the inner surface of the retaining ring can have othergeometries. For example, referring to FIGS. 8-12, the inner surface 130of the retaining ring can have a plurality of inwardly-extendingprojections 200. The projections can extend from a circle with a firstradius R1, inwardly to a circle with a smaller second radius R2 (shownin FIG. 8). Examples of geometries for the inner surface 130 includezig-zag, crenellated, trapezoidal and sinusoidal, although othergeometries are possible. There can be seven to one-hundred and fiftyprojections spaced around the inner surface of the retaining ring. Theprojections can be spaced at equal angular intervals around theretaining ring. Alternatively, the spacing between projections can vary,e.g., in a regular pattern.

For some implementations, e.g., as shown in FIGS. 8 and 10, eachprojection can be joined at its edges to its immediate adjacentprojections. For example, the region between each pair of adjacentprojections can include no flat or arced surface that is substantiallytangent to the circle defined by the first radius R1. FIG. 8 illustratesthe projections as triangular, but other geometries such as trapezoidal(shown in FIG. 10), sinusoidal (shown in FIG. 12) and semicircular arepossible. In addition, the inner tip of each projection and/or theintersection between each projection can be rounded.

For some implementations, e.g., as shown in FIGS. 9-11, the innermostportion of each projection 200 can be a flat surface 202, e.g., a flatfacet, at the inner second radius R2. For example, referring to FIG. 9,the projections 200 form a crenellated geometry, with the flat surface202 and flat side surfaces 206. A flat or curved region 204 of the innersurface can separate each projection 200 at the outer first radius R1.For the crenellated geometry, each flat surface 202 can intersect itsadjacent flat side surface 206 at about a 90° angle, e.g., at an able of85-90°.

Referring to FIGS. 10-11, the projections 200 are trapezoidal, with flatinner surface 202 and flat side surfaces 206. For the trapezoidalprojections 200, the angle between the flat outer surface 202 and theflat side surface 206 can be 115-145°. In FIG. 10, the projections 200are separated at the outer first radius R1 by flat or curved regions204, whereas in FIG. 11, each projection 200 is joined at its edges toits immediate adjacent projections without the flat or curved region204.

Referring to FIG. 12, the projections 200 can form an undulatingsurface, e.g., the bottom inner edge can form a serpentine path. Eachprojection can be a substantially sinusoidal curve. A potentialadvantage of this implementation is that the lack of sharp cornersbetween the projections can reduce the likelihood of slurry sticking anddrying in the corners, thus potentially reducing defects.

Referring to FIG. 13, portions of the inner surface 130 can havedifferent surface texture, e.g., different surface roughness, or surfacegrooving in different directions, e.g., vertical versus horizontalgrooving, or surface grooving with different depths. For example, theinner surface 130 can include arc segments 210 that have a differentsurface texture than arc segments 212. In some implementations, theportions, e.g., arc segments, with different surface texture arearranged in a regular pattern, e.g., an alternating pattern, such asalternating between smooth and rough, or alternating between horizontaland vertical grooving. There can be seven to one-hundred and fiftyportions spaced around the inner surface of the retaining ring. Theportions can be spaced at equal angular intervals around the retainingring. Alternatively, the spacing of the portions can vary, e.g., in aregular pattern. Each portion can have the same arc length, althoughthis is not required.

For example, the arc segments 212 can be rougher than the arc segments210. For example, the arc segments 212 can have an Ra roughness of 4 to2000 micro-inches, e.g., 8 to 64 micro-inches, whereas the arc segments210 can have an Ra roughness down to about 2 micro-inches.

As another example, referring to FIG. 14, the arc segments 212 can havegrooving in a different direction than the arc segments 210. Thegrooving direction of the arc segments 212 can be perpendicular to thegrooving direction of the arc segments 210, although other angles, e.g.,20° to 90°, are possible. In some implementations, e.g., as shown inFIG. 13, arc segments 210, 212 alternate between horizontal and verticalgrooving. However, other orientations are possible, e.g., alternatingbetween slanted diagonal-left and slanted diagonal-right. In addition,more complex patterns of three or more surface textures are possible.

The different surface textures described above can be applied to thefacets 150 or the projections 200 of the embodiment discussed above.Thus, different facets 150 and projections 200 can have differentsurface texture, e.g., different surface roughness, or surface groovingin different directions. Again, in some implementations, the facets orprojections with different surface texture are arranged in a regularpattern, e.g., an alternating pattern, such as alternating betweensmooth and rough texturing, or alternating between horizontal andvertical grooving.

Although in the various embodiments above the portion 132 of the innersurface 130 that is adjacent the bottom surface 120 is vertical(perpendicular to the polishing surface), this portion 132 of the innersurface 130 could be tilted, e.g., at an angle up to 30° off vertical.

In addition, referring to FIG. 15, the portion 132 of the inner surface130 that is adjacent the bottom surface 120 can have portions withdifferent inclination. For example, the inner surface 130 can includefacets or arc segments 220 that have a different angle of tilt relativeto the horizontal plane than facets or arc segments 222. In someimplementations, the portions, e.g., facets or arc segments, arearranged in a regular pattern, e.g., an alternating pattern. Forexample, as shown in FIG. 15, the facets or arc segments 220 are tiltedoutwardly (from bottom to top), whereas the facets or arc segments 222are tilted inwardly (from bottom to top). However, other combinationsare possible, e.g., vertical versus tilted, or small tilt angle versuslarge tilt angle. There can be seven to one-hundred and fifty portionsspaced around the inner surface of the retaining ring. The portions canbe spaced at equal angular intervals around the retaining ring, or thespacing of the portions can vary, e.g., in a regular pattern.

The different tilt angles of the surface described above can be appliedto the facets 150 or the projections 200 of the embodiment discussedabove. Thus, different facets 150 and projections 200 can have differenttilt angles. The variations in tilt angle can also be combined with thevariations in surface texture.

Referring to FIG. 16, the portion of the retaining ring having the innersurface 132 that contacts the substrate can be an insert 106 that fitsinto a recess in a ring 108 that extends both above and radially outwardof the insert 106. If the inner surface 132 becomes damaged or worn fromextended use, the insert 106 can be replaced with a new insert 106.

The retaining ring can be formed of two or more stacked regions ofdifferent materials, or be a single unitary ring of homogenouscomposition, e.g., a solid plastic ring. The channels, if present, canbe aligned to regular points of the features, or different channels canintersect different points on the features. The channels, if present,can cover anywhere from 5% to 90% of the bottom surface of the retainingring. The outer surface of the retaining ring can include steps or lips,or be a single vertical cylindrical or frustoconical surface. Theconcepts are applicable to retaining ring of different sizes, e.g.,retaining rings for substrates of 4 to 18 inch diameter, or larger.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other implementations are within the scope of the followingclaims.

What is claimed is:
 1. A method of forming a retaining ring, comprising:joining an upper portion of the retaining ring having a frustoconicalinner surface to a lower portion of the retaining ring having acylindrical inner surface; and machining the inner surface of the lowerportion and the inner surface of the upper portion to form a pluralityof flat facets that intersect the frustoconical inner surface at aplurality of curved edges.
 2. The method of claim 1, comprisingmachining the inner surface of the lower portion and the inner surfaceof the upper portion such that a lowest point on each curved edge isaligned to a boundary between the upper portion and the lower portion.3. The method of claim 1, comprising machining the inner surface of thelower portion and the inner surface of the upper portion such that alowest point on each curved edge is above a boundary between the upperportion and the lower portion.
 4. The method of claim 1, wherein joiningcomprises one or more of adhering with an adhesive, connecting with amechanical fastener, or fixing with a dovetail joint.
 5. The method ofclaim 4, wherein joining comprises adhering with an adhesive.
 6. Themethod of claim 1, wherein the lower portion is composed of a firstmaterial and the upper portion is composed of a second material that ismore rigid than the first material.
 7. The method of claim 6, whereinthe first material is plastic and the second material is metal.
 8. Themethod of claim 1, wherein the lower portion and the upper portion arecomposed of the same material.
 9. The method of claim 1, comprisingforming the lower portion by injection molding.
 10. The method of claim9, comprising forming a plurality of channels in a bottom surface of thelower portion.
 11. The method of claim 1, comprising machining the innersurface of the lower portion and the inner surface of the upper portionto have between 10 and 150 facets.
 12. The method of claim 1, comprisingmachining the inner surface of the lower portion and the inner surfaceof the upper portion such that the plurality of flat facets intersect abottom surface of the lower portion to form a polygonal inner perimeterof the bottom surface.
 13. The method of claim 12, comprising machiningthe inner surface of the lower portion and the inner surface of theupper portion such that the plurality of flat facets are perpendicularto the bottom surface of the lower portion.